1. Field of the Invention
The present invention relates to a motor control apparatus used for an electric power steering system for a vehicle or the like, and more specifically to a motor control apparatus that controls a motor current in a feedback manner so as to make a motor current detected value (detected current) coincide with a motor current command value (target current). In particular, the invention relates to a novel improved or advanced technology to perform an abnormality determination in an effective manner.
2. Description of the Related Art
There has been known a motor control apparatus which determines that a motor is in an abnormal state, when a current deviation between a motor current detected value as measured and a motor current command value as stored exceeds a predetermined determination threshold, and sets the motor current command value to “0” thereby to interrupt the output of the motor (see, for example, a first patent document: Japanese examined patent application publication No. H06-29031).
In the known motor control apparatus described in the above-mentioned first patent document, when the motor of the permanent magnetic field type performs power running, a counterelectromotive force is generated in a direction to reduce the motor current, so the feedback control of the motor current tends to undershoot. As a result, a normal operation state and an abnormal state (a short fault of armature windings, a ground fault of wiring between the control apparatus and the motor, etc.) can be identified easily.
In the known motor control apparatus, an abnormality determination can be made when the motor power runs, but a counterelectromotive force is generated in a direction to increase the motor current, for example, when the motor performs a regeneration operation, or when the motor is driven to rotate in a direction opposite to the direction of its output torque for regeneration under the influence of external torque disturbances applied to the motor in spite of a power running instruction given. As a result, the motor current, even if controlled in a feedback manner, tends to overshoot, thus giving rise to a problem that there is a possibility of making a misdetermination that the motor current is abnormal.